Art of cracking hydrocarbons



July 11, 1939. v H. L. PELZER 2,155,725

ART OF CRACKING HYDROGARBONS I Filed April 4, 1930 I INVENTOR //arr L,Pe/zer PAM, QWZ M rLQQMWQ ATTORNEY5 Patented July 11, 1939 PATENT OFFICEART OF CRACKING HYDROCARBONS poration of Maine Harry L. Pelzer, Houston,Tex, assignor to Sinclair Refining Company, New York, N. Y., a cor-Application April 4, 1930, Serial No. 441,649

4 Claims.

This invention relates to improvements in the manufacture of lowerboiling hydrocarbon oils, such as'gasoline, from higher boilinghydrocarbon oils, such as gas oil and reduced crude oil, {:5 by crackingoperations. This invention provides improvements, in both methods andapparatus for heating oil to cracking temperatures, which areadvantageous in several respects butparticularly in that they affordmethods andap'pa- 10 ratus by which the temperaturegradient of the oilpassing thru the heating operation may be given almost any desiredcharacteristics atthe choice of the operator, both effectively andefliciently. T 1

M The development of cracking operations in which oil is subjected tosevere cracking conditions to produccmo'tor fuel gasoline of improvedanti-knock properties has developed, as an element of increasingimportance, a requirement .39 for more precisecontrol of the temperaturegraclient of the oil passing thrutheheatin'g operationand for themaintenance of temperature gradients having characteristics not to beobtained by the more simple heater arrangements andheating operationspreviously used. This invention is of general application in meetingthese requirementsin conjunction with various types of crackingoperations.

This invention, however, is of special value 59 and application incarrying out operations in which high boiling oil is heated to acracking temperature under high pressure and in which the hot oilproducts of this heating operation are separated into a vaporizedfraction and an unvaporizedfraction under lower pressure, or socalledpressure coil. cracking operations, This inventionisalso of. value andapplication in carrying outoperations'in which high boiling oil isheated to a high cracking temperature substantially inthe vapor phase.

In oneaspect, this invention is a modification of: the inventiondescribed in my application filed April 4, 1930, Serial No. 441,648,upon which Patent No. 1,845,554 was granted February'lfi, 1932. Incarrying out the method of this invention, heating gases from a fire-boxin which fuel is burned are passed successively over a first battery anda second battery of heating tubes, a part of the heating gases whichhave passed over both batteries of heating tubes is recirculated overthe second battery of heating tubes together with the heating gaseswhich have passed iii? over the first battery of. heating tubes and apart,

g of the heating gases fresh from the fire-box, the

heating gases fresh from the fire-box reheating,

by direct heat exchange, the recirculated heating gases before themixture of heating gases is passed over the second battery of heatingtubes,

and oil is passed thru one and then the other J of the batteries ofheating tubes and heated to a cracking temperature during passagetherethru. To provide for tempering of the heating gases fresh from thefire-box before they first contact with the heating tubes'of the firstbattery, another part of the heating gases which have passed over bothbatteries or heating tubes may be recirculated over both batteries of.heating tubes together with the heating gases fresh from the fire-box.

Thus, according to the invention, almost any desired temperaturegradient may be maintained with respect to the oil passing thru theheating tubes. The heating gases recirculated over the second battery ofheating tubes may be heated, by admixture with heating gases fresh fromthe fire-box, to a temperature the same as or higher than that at whichthe heating gases from the fire-box first contact with the heating tubesof the first battery. The extremely flexible control of the temperaturegradient of, the heating gases during their passage over the heatingtubes thus afi'orded makes possible, in conjunction with control of therate of oil circulation and the direction of oil circulation thru theheater, the maintenance of almost any desired temperature gradient ofthe oil passing thru the heater,

The oil may be passed thru the batteries of heating tubes generallycountercurrent to the flow of heating gases thereover or generallyconcurrent with the fiow of heating gases thereover, or the oil may bepassed thru part of the heating tubes countercurrent to and thru partof. the heating tubes concurrent with the flow of heat ing gases overthe heating tubes. One of the advantages of the invention, however, isthat it makes possible elimination of inversions and reinversions of thedirection of oil flow in passage thru the heater without sacrifice withrespect to flexibility of control. Thus, according to the invention,almost any desired temperature gradient of the oil passing thru theheater may be maintained with simple continuous flow of the oil thru theheater, either generally countercurrent to or generally concurrent withthe flow of heating gases.

According to the invention, oil flowing thru the heater may be broughtrapidly to a high cracking temperature and then maintained atsubstantially the same temperature for a further period in the heater,or it may be brought rapidly to a high cracking temperature and thenmaintained at a temperature increasing at a slower rate andapproximately uniformly with respect to time for a further period in theheater, or it may be heated to a temperature, ultimately a crackingtemperature, progressively increasing but increasing at a diminishingrate while flowing thru the heater, for example.

The apparatus of the invention comprises a heating flue and heatingtubes arranged in the heating flue, a fire-box communicating thru aprimary passage with one end of the heating flue and thru a secondarypassage with an intermediate part, or with several intermediate parts,of the heating flue, means for forcing heating gases withdrawn from theother end of the heating flue into the intermediate part, or parts, ofthe heating flue, and means for forcing oil thru the heating tubes.

The invention will be further described in connection with theaccompanying drawing which illustrates, diagrammatically andconventionally, in elevation and partly in section and with parts brokenaway, one form of apparatus embodying the invention and adapted forcarrying out the invention.

Referring to the drawing, the apparatus illustrated comprises a furnaceincluding a firebox I and a heating flue 2, a flue 3 connecting thefire-box I with the upper end of the heating flue 2 and a stack flue 4communicating with the lower end of the heating flue 2, ducts 5, 6 and Iincluding a fan 8 for recirculating heating gases withdrawn from thelower end of the heating flue 2 thru the lower part of the heating flue2 by Way of the duct 6 and thruout the heating flue 2 by wayof the ductI. Dampers are provided, as illustrated, in the ducts 6 and l and in thestack 9 for controlling the recirculation and discharge of heating gasestherethru. Two or more batteries of heating tubes, connected in seriesto form a continuous heating conduit, are arranged in the heating flue 2and a pump I0 is provided for forcing oil thru the heating tubes. Theoil is supplied to the heating tubes thru the connection II and the hotoil products are discharged therefrom thru the connection I2 in theapparatus illustrated. The oil may likewise be supplied to the heatingtubes thru the connection I2 and discharged therefrom thru theconnection I I, or it may be supplied to the second battery of heatingtubes I3 thru the connection I2, passed from the second battery to thefirst battery of heating tubes I4 thru the connections I5 and II anddischarged from the second battery of heating tubes thru the connectionI6. In carrying out so-called pressure coil cracking operations in theapparatus illustrated, thep-ressure in the heater may be maintained andregulated by means of the valve IT, and an oil cooler than the hot oilproducts discharged thru the connection I2 may be introduced thru theconnection I8 to arrest the cracking reaction initiated in the heater.The hot oil products may be discharged thru the connection I9, in thecase of so-called pressure coil cracking operations, for example, to anysuitable evaporator for the separation of vaporized and unvaporizedfractions, or, in the case of vapor phase cracking operations, to a tarseparator.

The heating gases recirculated over the second battery of heating tubesI3 are introduced into the heating flue 2 thru the duct 6 intermediatethe first battery of heating tubes I4 and the second battery I3. A partof the heating gases fresh from the fire-box I is also introduced intothe heating flue 2 intermediate the first battery of heating tubes I4and the second battery I3 thru the duct 20. The duct 20 is also providedwith a damper for controlling the circulation of heating gasestherethru. A pair of baflles 2| are provided in the intermediate part ofheating flue 2 above the second battery of heating tubes I3 to promoteintermixture of the recirculated heating gases introduced thru the duct6, the heating gases fresh from the fire-box introduced thru the duct20, and the heating gases which have passed over the first battery ofheating tubes I4. This intermixture of these gases results in reheatingthe recirculated heating gases introduced thru the duct 6 before theresulting mixture passes over the second battery of heating tubes I 3.By regulating the rates of introduction of the recirculated heatinggases and the heating gases fresh from the fire-box into theintermediate part of the heating flue 2 thru the ducts 6 and 20, therecirculated heating gases may be reheated to a temperature higher thanthat of the heating gases fresh from the fire-box as they first contactwith the heating tubes of the first battery I4. It will be understoodthat one or more ducts corresponding to the duct 6 may be providedconnecting theduct 5 with several intermediate parts of the heating flue2 and, similarly, that one or more ducts corresponding to the duct 20may be provided connecting the flue 3'with several intermediate parts ofthe heating flue 2.

That part of the heatinggases withdrawn from the lower end of theheating flue 2 and not recirculated thru the heating flue 2 isdischarged thru the stack flue.9. Fuel for combustion is supplied to thefire-box, in the apparatus illustrated, by means of the burner 22.Preheated air, preheated by heat exchange with the waste heating gasesescaping thru the stack 9, may be supplied to the fire-box I forcombustion.

In the apparatus illustrated, the rate of heat transfer in the lower'part of the heating flue 2 is improved because of the increasedvelocity of flow of heating gases therethru resulting from the increasein volume of the heating gases flowing therethru because of therecirculation of the heating gases introduced into the intermediate partof the heating flue. The heating tubes in the upper part of the heatingflue 2, which are he first to contact with the heating gases fresh fromthe fire-box, may be protected by tempering these heating gases freshfrom the fire-box with heating gases withdrawn from the lower end of theheating flue 2'and recirculated therethru thru the ducts 5 and I. Theheating tubes may, with advantage, as in the apparatus illustrated, beprotected from direct radiation from the fire-box by'the provision of anappropriate bridge wall and appropriate baflles, such as bafile 23beneath the duct 20, as illustrated.

I claim:

1. In heating oil to cracking temperatures in cracking operations, theimprovement which comprises passing heating gases from a firebox inwhich fuel is burned successively over a first battery and a secondbattery of heating tubes, recirculating part of the heating gases whichhave passed over both batteries of heating tubes over the second batteryof heating tubes together with the heating gases which have passed overthe first battery of'he'ating tubes and heating gases fresh from thefire-box, thereby reheating the recirculated heating gases by directheat exchange with the heating gases fresh from the fire-box before themixture of heating gases is passed over the second battery of heatingtubes, and passing oil thru one of the batteries of heating tubes andthen thru the other and heating it to a cracking temperature therein.

2. In heating oil to cracking temperatures in cracking operations, theimprovement which comprises passing heating gases from a fire-box inwhich fuel is burned successively over a first bat tery and a secondbattery of heating tubes, recirculating part of the heating gases whichhave passed over both batteries of heating tubes over the second batteryof heating tubes together with the heating gases which have passed overthe first battery of heating tubes and heating gases fresh from thefire-box, thereby reheating the recirculated heating gases by directheat exchange with the heating gases fresh from the fire-box to atemperature higher than that of the heating gases from the fire-box asthey first contact with the heating tubes of the first battery beforethe mixture of heating gases is passed over the second battery ofheating tubes, and passing oil thru one of the batteries of heatingtubes and then thru the other and heating it to a cracking temperaturetherein.

3. In apparatus for heating oil to cracking ternperatures, incombination, a heating flue and heating tubes arranged therein, afire-box communicating thru a primary passage with one end of saidheating flue and thru a secondary passage with an intermediate part ofsaid heating flue, means for forcing heating gases withdrawn from theother end of said heating flue into said inter mediate part, and meansfor forcing oil thru said heating tubes.

4. An oil heating furnace comprising a combustion space, a heatingspace, a flue, connections for passing gases from said flue to saidheating space and to said combustion space, comprising conduitsconnecting said flue and said combustion space and heating space, anddampers in said conduits.

HARRY L. PELZER.

